Growth and decline of a penguin colony and the influence on nesting density and reproductive success

Colonial breeding is characteristic of seabirds but nesting at high density has both advantages and disadvantages and may reduce survival and fecundity. African penguins (Spheniscus demersus) initiated breeding at Robben Island, South Africa in 1983. The breeding population on the island increased in the late 1990s and early 2000s before decreasing rapidly until 2010. Before the number breeding peaked, local nest density in the areas where the colony was initiated plateaued, suggesting that preferred nests sites were mostly occupied, and the area used by breeding birds expanded. However, it did not contract again as the population decreased, so that nesting density varied substantially. Breeding success was related positively to the prey available to the breeding birds and negatively to local nest density, particularly during the chick-rearing period, suggesting a density-dependence operating through social interactions in the colony, possibly exacerbated by poor prey availability when the breeding population was large. Although nest density at Robben Island was not high, nesting burrows, which probably reduce the incidence of aggressive encounters in the colony, are scarce and our results suggest that habitat alteration has modified the strength of density-dependent relationships for African penguins. Gaining a better understanding of how density dependence affects fecundity and population growth rates in colonial breeders is important for informing conservation management of the African penguin and other threatened taxa.     

Acoustic activity across a seabird colony reflects patterns of within-colony flight rather than nest density

Passive acoustic monitoring is increasingly being used as a cost-effective way to study wildlife populations, especially those that are difficult to census using conventional methods. Burrow-nesting seabirds are among the most threatened birds globally, but they are also one of the most challenging taxa to census, making them prime candidates for research into such automated monitoring platforms. Passive acoustic monitoring has the potential to determine presence/absence or quantify burrow-nesting populations, but its effectiveness remains unclear. We compared passive acoustic monitoring, tape-playbacks and GPS tracking data to investigate the ability of passive acoustic monitoring to capture unbiased estimates of within-colony variation in nest density for the Manx Shearwater Puffinus puffinus. Variation in acoustic activity across 12 study plots on an island colony was examined in relation to burrow density and environmental factors across 2 years. As predicted fewer calls were recorded when wind speed was high, and on moon-lit nights, but there was no correlation between acoustic activity and the density of breeding birds within the plots as determined by tape-playback surveys. Instead, acoustic indices correlated positively with spatial variation in the in-colony flight activity of breeding individuals detected by GPS. Although passive acoustic monitoring has enormous potential in avian conservation, our results highlight the importance of understanding behaviour when using passive acoustic monitoring to estimate density and distribution.     

Vegetation characteristics influence fine-scale intensity of habitat use by wild turkey and white-tailed deer in a loblolly pine plantation

Habitat quality is often evaluated based on food availability. However, ecological theory suggests cover should be a more important decision rule when food is not a proximate threat to fitness, as cover mediates predation risk as well as other important factors of fitness. In reality, vegetation characteristics related to food availability and cover are rarely coupled with animal use in the same space and time to determine their relative influences on habitat use. Using an array of 81 camera traps in a matrix of forest management strategies used to deliberately cause a wide disparity in vegetation characteristics, we monitored intensity of use by white-tailed deer (Odocoileus virginianus) and wild turkey (Meleagris gallopavo). We measured vegetation characteristics related to food and cover at each camera trap location then used a generalized additive model to determine how vegetation characteristics specific to the location affected intensity of habitat use by animals at the location. Consistent among both species, cover best explained intensity of habitat use. Contrastingly, food did not explain intensity of habitat use well for either species. Some vegetation simultaneously provides cover and food, and our data indicate that areas with vegetation characteristics providing both resources had the greatest influence on intensity of habitat use by both species. Our results suggest deer and turkey may perceive cover as a more important habitat component when food is not a proximate fitness threat.     

Tick infestation of chicks in a seabird colony varies with local breeding synchrony,local nest density and habitat structure

Parasites are a major risk for group‐living animals and seabirds are notoriously susceptible to ectoparasite infestations because they commonly nest in dense colonies. Ticks parasitize seabirds across all biogeographical regions and they can be particularly harmful to nestlings, but the ecological factors that affect their transmission to chicks are little studied and poorly understood. Here we show that abundance of tick larvae in blue‐footed booby Sula nebouxii broods varies with local nest synchrony and density, and also with habitat structure: abundance increased with local breeding synchrony, was linearly and quadratically related to local nest density, and was highest toward the southern end of the study area which has suitable (boulder‐rich) habitat for ticks. Also, with increasing chick age infestation first increased and then declined. The results of this study highlight how local physical and social environmental factors influence infestation of seabird nestlings by ticks.     

Nest site selection and nesting success of five species of passerines in a South American open Prosopis woodland

I analyzed nest site preferences and whether these preferences were linked to nest success of five bird species breeding in an arid area of southern South America. Most nests (90%) were located in three plant species (Geoffroea decorticans, Capparis atamisquea, and Atriplex lampa). Serpophaga griseiceps, Poospiza ornata, and P. torquata nested in plants with size significantly different from randomly selected plants. At the mesohabitat scale (i.e., habitat patch surrounding the nest), four species showed clear differences from random patches within the general habitat, and the remaining species (Saltatricula multicolor) showed a non-significant trend. The daily survival rate of S. griseiceps nests placed in the preferred plant species (i.e., G. decorticans) was lower than those in the other nest-plants. In the other four bird species, nest survival did not differ between preferred and other plants used for nesting. At the scale of microhabitat (i.e., plant size and location of the nest inside the plant), no significant differences were detected between unsuccessful and successful nests. Similarly, unsuccessful nest patches did not differ significantly in habitat features from those that were successful. High nest predation rates found in this habitat (around 85% for the total assemblage) and a relatively high diversity of predators (and of predation tactics) appear to impede the presence of safe sites for nesting (i.e., there are trade-offs between avoidance strategies).     

Temporal variation in habitat use by nekton in a subtropical estuarine system

Utilisation by fish of different estuarine habitats is known to vary at many different temporal scales, however no study to date has examined how utilisation varies at all the relevant times scales simultaneously. Here, we compare the utilisation by fish of sandy, intertidal foreshore habitats in a subtropical estuary at four temporal scales: between major spawning periods (spring/summer and winter), among months within spawning periods, between the full and new moon each month, and between night and day within those lunar phases. Comparisons of assemblage composition, abundance of individuals and of fish in seven different ‘ecological guilds’ were used to identify the temporal scales at which fish varied their use of unvegetated sandy habitats in the lower Noosa Estuary, Queensland, Australia. Fish assemblages were sampled with a seine net at three different regions. The most numerically dominant species caught were southern herring (Herklotsichthys castelnaui: Clupeidae), sand whiting (Sillago ciliata: Sillaginidae), weeping toadfish (Torquigener pleurogramma: Tetraodontidae), and silver biddy (Gerres subfasciatus: Gerreidae). Considerable variation at a range of temporal scales from short term (day versus night) to longer term (spawning periods) was detected for all but one of the variables examined. The clearest patterns were observed for diurnal effects, where generally abundance was greater at night than during the day. There were also strong lunar effects, although there were no consistent patterns between full moon and new moon periods. Significant differences among months within spawning periods were more common than differences between the actual spawning periods. The results clearly indicate that utilisation of sandy, unvegetated estuarine habitats is very dynamic and highly variable in space and time.     

Winter density and habitat preferences of three declining granivorous farmland birds: The importance of the keeping of poultry and dairy farms

Populations of granivorous farmland birds have dramatically declined during recent decades in many European countries. Winter conditions and consequently, survival rates of farmland bird species during this critical period, are considered as one of the main causes of this negative trend. However, the importance of different habitat structures and connected food sources for successful overwintering in bird species has gained little attention so far in the Czech Republic. In this study we aimed to examine the role of habitat composition and food availability on winter distribution and abundance of three declining sedentary and granivorous bird species. During the winters 2009–2014, 149 villages in the Czech Republic were monitored for distribution and density of three farmland seed-eaters. House Sparrow was the most dominant species (88.6% of villages occupied; 4.32 ± 4.67 ind./100 m of transect), followed by Tree Sparrow (67.1% villages occupied; 1.83 ± 3.53 ind./100 m of transect) and Collared Dove (65.8% villages occupied; 0.72 ± 1.51 ind./100 m of transect). Occurrence of House and Tree Sparrow was significantly affected by the number of instances of poultry keeping. In both species, occupied villages showed a higher number of instances of poultry keeping. We did not find any such significant relationship for Collared Dove. Density of House Sparrow was significantly higher in villages with dairy farms, but we failed to find this relationship for Tree Sparrow and Collared Dove. Habitat preferences were similar for all three studied species. They positively responded to the proportion of shrubs/trees, the keeping of poultry, dairy farms and they avoided houses, arable land and grasslands. We conclude that poultry keepings and dairy farms can be important for studied species during the winter since they offer high food availability and good protection against predators. This suggestion is supported by the fact that long-term population decline has coincided with a long-term reduction in the keeping of poultry and dairy farms in the Czech Republic during the last 50 years.     

Preservation of genetic diversity in a wild and captive population of a rapidly declining mammal,the Common hamster of the French Alsace region

The Common hamster (Cricetus cricetus) faced massive population declines throughout its western range margin. In France, relict populations remained in the Alsace region. By comparing allelic diversity using microsatellite analysis over a time span of 12 years we investigated if this population decline led to genetic erosion in a French relict population of the species. Genetic diversity was moderate but comparable to other populations from Western Europe. Interestingly, no decline of allelic variation was revealed between 1999 and 2012 in the study region (expected heterozygosity = 0.51 in 1999 and 0.5 in 2012, respectively), suggesting a sufficiently high effective population size of ∼500 (179–956 SD). While several alleles were lost in a captive breed maintained for restocking purposes in the region, expected heterozygosity was comparably high (=0.5). Our results show that genetic diversity has been effectively maintained in a relict population of French Common hamsters despite of massive range loss. We recommend the maintenance of intense in situ conservation effort, along with regular monitoring of genetic diversity and effective population size.     

Finding your mate in a seabird colony: contrasting strategies of the Guillemot Uria aalge and King Penguin Aptenodytes patagonicus

Capsule King Penguins recognize their mates by voice, but Guillemots do not need acoustic cues even though their calls show individual variation.

Aims To determine whether the structure of Guillemot calls could allow individual recognition, as with King Penguin, and whether acoustic cues are used to locate mates among a dense mass of conspecifics at a colony.

Methods Observations were made on breeding Guillemots and King Penguins. Calls made by birds returning to their mates were recorded, the signals digitized and the calls analysed. Calls were later played back to the mates of the birds concerned and the effects noted on both them and their neighbours.

Results Both Guillemots and King Penguins emitted calls on return to the breeding site which contained individual signatures and were therefore potentially usable for mate recognition. In King Penguins, auditory recognition was essential for finding a mate, whereas in Guillemots most of the arriving birds located their mate in a dense crowd of conspecifics without the help of acoustic signals. Guillemots could differentiate neighbours from strangers without auditory cues.

Conclusion Calls are essential for the successful identification of mates by King Penguins but not by Guillemots.     

Breeding dispersal in a heterogeneous landscape: the influence of habitat and nesting success in greater snow geese

Despite numerous studies on breeding dispersal, it is still unclear how habitat heterogeneity and previous nesting success interact to determine nest-site fidelity at various spatial scales. In this context, we investigated factors affecting breeding dispersal in greater snow geese (Anser caerulescens atlanticus), an Arctic breeding species nesting in two contrasting habitats (wetlands and mesic tundra) with variable pattern of snowmelt at the time of settlement in spring. From 1994 to 2005, we monitored the nesting success and breeding dispersal of individually marked females. We found that snow geese showed a moderate amount of nest-site fidelity and considerable individual variability in dispersal distance over consecutive nesting attempts. This variability can be partly accounted for by the annual timing of snowmelt. Despite this environmental constraint, habitat differences at the colony level consistently affected nesting success and settlement patterns. Females nesting in wetlands had higher nesting success than those nesting in mesic tundra. Moreover, geese responded adaptively to spatial heterogeneity by showing fidelity to their nesting habitat, independently of snowmelt pattern. From year to year, geese were more likely to move from mesic to high-quality wetland habitat, regardless of previous nesting success and without cost on their subsequent nesting performance. The unpredictability of snowmelt and the low cost of changing site apparently favour breeding-site dispersal although habitat quality promotes fidelity at the scale of habitat patches.     

Recent papyrus swamp habitat loss and conservation implications in western Kenya

Papyrus Cyperus papyrus swamps are characteristic of many wetlands of tropical Africa. Like most wetland habitats worldwide, they are under human pressure due to harvesting and reclamation for agriculture. Changes in papyrus cover were assessed using aerial photographs at three Important Bird Areas (IBAs) in the Kenyan sector of Lake Victoria. Papyrus area losses of 50% (Dunga), 47% (Koguta) and 34% (Kusa) occurred between 1969 and 2000. The habitat loss and degradation at the sites appeared purposeful, driven by demand for agricultural land and other papyrus products. Cleared papyrus and cultivated areas around all sites increased over the same period. If papyrus habitat loss continues at current rates, papyrus swamps at Dunga and Koguta will disappear by 2020, and Kusa will be reduced to only 19% of its 1969 area. Human population growth around the sites, with concomitant increase in land use activities and papyrus harvesting are the major factors that account for papyrus area reductions. Loss of total habitat is accompanied by deterioration in habitat quality within remaining areas. Papyrus physical structure (height and density) inversely correlate to human disturbances that include footpaths, cutting, burning, grazing and farming. The continued papyrus habitat loss and degradation represents a significant threat to biodiversity conservation particularly for papyrus-specialist birds and other papyrus-reliant species in western Kenya. The observed pattern of papyrus extents and land use changes at all sites provide the site-scale information necessary for papyrus conservation planning. In particular, conservation action is needed most urgently at Dunga and Koguta as they face severe land use pressures.     

Influences of habitat features and human disturbance on use of breeding sites by a declining population of southern fur seals (Arctocephalus australis)

Southern fur seals Arctocephalus australis in Peru have declined gradually over the past decade, and declined dramatically (72%) as a result of low food availability during the severe El Niño in 1997–98. In 1999, seals abandoned some historically important breeding sites. This is particularly alarming because new sites were not colonized. Our objective was to examine how habitat features and human disturbance influenced whether sites were currently used, abandoned or apparently not used in the past by fur seals for breeding. Data were collected on 14 variables at 70 potential breeding sites at three guano reserves in Peru. Discriminant analysis revealed significant multivariate differences among sites currently used for breeding, abandoned sites and unused sites ( F =5.97, P <0.00001), and the model classified 74% of sites correctly. Currently used sites were less likely to have human disturbance and more likely to have offshore islands, stacked rocks, tide pools and abundant shade. Separate discriminant analyses for each reserve produced similar results. Habitat associated with thermoregulation (e.g. shade or pools) may be more important to fur seals in Peru, which breed at lower latitudes and are at greater risk of overheating on land than other populations. Habitat with minimized human access may be especially important to seals in small populations in which individuals may perceive themselves as more vulnerable because of decreased vigilance and dilution effects. Seals in our study selected breeding habitat with stacked rocks, which create shade and tide pools for thermoregulation and make human access difficult; but pups might suffer higher mortality in this habitat. We hypothesize that fur seals in Peru may exhibit an Allee effect, whereby suitability of habitat varies with population abundance.     

Changes in land use and habitat availability affect the population genetic structure of Metrioptera roeselii (Orthoptera: Tettigoniidae)

The impact of temporal changes in habitat availability and land use on the present genetic diversity of the grassland katydid species Metrioptera roeselii was investigated in an extensively used agricultural landscape (Lahn-Dill-Bergland, Germany) based on six microsatellite loci. By integrating spatial and temporal dimensions, this study contrasts to conventional approaches that usually record landscape changes at discrete points in time. Molecular data suggest little geographical substructuring of the species. Nevertheless, time-dependent effects on genetic diversity in terms of observed heterozygosity and allelic richness within subpopulations were detected by general linear models (GLM), explaining up to 82 and 13%, respectively. The results indicated that allelic richness was significantly reduced with higher rates of land-use change. Contrastingly, the level of heterozygosity even increased with increasing land-use change, if this rate increase was accompanied by a reduction in grassland amount, while with an increase of grassland amount the level of heterozygosity remained similar. Furthermore, depending on the study site, heterozygosity was differently affected by grassland age of sampled patches and of the surrounding. This is presumably induced by contrasting levels of heterozygosity in combination with differing modes of dispersal due to habitat availability and site-specific matrix effects. The loss of genetic diversity due to frequent land-use change might result in a reduced ability to adapt to landscape change, which is even more relevant in intensively used agricultural landscapes and in the course of climate change.     

Thermoregulation as a limit to habitat use in alpine marmots (Marmota marmota)

Summary The body temperature (T _b) of free-living alpine marmots rose with activity; the higher the effective environmental temperature (T _e), the higher the rise. Maximum T _bof 40° C was reached at the time of greatest activity in late afternoon or evening. The activity pattern was strongly influenced by the microclimate. Up to an T _eof 25° C the animals spent more time above ground and were more active the higher T _ewas, but above 25° C this trend was reversed, and the animals withdrew increasingly into their burrows. On warm days the activity pattern was therefore bimodal and above ground presence was reduced, in contrast to cool days. Hence behavioural thermoregulation limits the available time for above ground activity on days with high T _ein this strictly diurnal species. We suggest that the alpine marmots' preference for south oriented slopes is due to the better conditions for hibernation there, the microclimate during summer is more favourable on northerly slopes. Thermoregulatory constraints could also keep alpine marmots away from lower elevations.     

Predation of Lapwing Vanellus vanellus nests on lowland wet grassland in England and Wales: effects of nest density, habitat and predator abundance

There is concern that predation of Lapwing Vanellus vanellus nests may create additional pressure on declining populations of this species in Europe. At seven sites in England and Wales, daily nest predation rates on 1,390 nests were related to variables using Generalised Linear Mixed Models. The strongest predictor was Lapwing nest density (number of nests within 100 m): predation rates declined as nest density increased. Since nocturnal species, probably mammals, have been identified as the major predators of Lapwing nests at these sites, these results suggest that Lapwings are able to deter mammalian predators or may settle to nest at high densities in areas with low predation pressure. At the site level, there was no relationship between Lapwing nesting density and fox density, and a positive relationship with Carrion Crow Corvus corone nesting density. There was a weaker effect of distance to field boundary: nests closer to boundaries were more likely to be predated. Weak interactive effects between crow density and both nest visibility and distance to vantage point were identified in models using a reduced subset of nests. These were counter-intuitive, did not persist in the larger data set, and do not have obvious explanations. If Lapwings nesting at high density are able to deter predators, there are implications for land management. Smaller areas could be managed within potential breeding habitat to encourage Lapwings to nest in dense colonies. Selection of larger fields for such management, where nests could be located far from the field boundary should improve the value of such measures.     

Use of time‐lapse photography and digital image analysis to estimate breeding success of a cliff‐nesting seabird

Development of new methods for obtaining basic demographic data from difficult‐to‐access breeding colonies and easily disturbed species is an important challenge in studies of seabirds. We describe a method that can generate data concerning annual breeding success of cliff‐nesting seabirds or other colonial birds with open nests. Our method requires only a single visit to a colony every second or third year, and is based on the use of automated time‐lapse photography. To test our method, we used time‐lapse photos to examine the breeding success of Thick‐billed Murres (Uria lomvia) in two breeding colonies in Greenland during the years 2011, 2012, and 2014. Based on the analysis of time‐lapse photos, we found that hatching success during the 3 yr of our study ranged from 60% to 81%, fledging success from 89% to 95%, and breeding success from 53% to 74% (Table 1). Use of digital image analysis made it possible to differentiate between breeding and non‐breeding birds and determine if and when breeding attempts failed or succeeded. The key to making our method a realistic long‐term monitoring technique is the use of an automated, formal image analysis to process the thousands of photos from the time‐lapse cameras and, more specifically, to reduce a large number of photos to a manageable number. Using our method, we needed 12–22 h per study plot, depending on the number of breeding sites per plot (range = 47–127) and whether it was the first or the second time the plot was analyzed, to obtain our estimates of hatching, fledging, and breeding success. This included time for data preparation, image analyses, visual inspections, and summarizing data in a spreadsheet. We found that our estimates of breeding success were comparable to those obtained by direct observation in the field. An important aspect of using time‐lapse technology is to foresee potential reasons why time‐lapse cameras might stop taking pictures, for example, equipment failure (camera, timer, or battery) or interference by visitors (e.g., vandalism or theft). As such, thorough testing of time‐lapse systems and selecting camera locations less likely to be disturbed are most important. We believe that use of time‐lapse photography in combination with digital image analysis to estimate breeding success can be useful for determining the breeding success of other cliff‐nesting seabirds and, more generally, other birds that breed in colonies, especially those located in remote areas and where direct observation may disturb birds.     

Processes regulating early post-settlement habitat use in a subtidal assemblage of brachyuran decapods

In highly mobile animals post-settlement dispersion of juveniles can strongly influence the observed patterns of abundance and distribution. To explore the relative importance of factors regulating the use of habitat by crabs we performed a multi-species manipulative experiment in a subtidal environment of the central Chilean coast. First, demographic patterns were established by performing a year-round crab survey in three discrete and well-known subtidal crab habitats: (1) algal turf, (2) cobbles and (3) shell hash. Second, habitat preferences were experimentally evaluated using concrete trays that were filled with different substrate types that simulate natural habitats. Settlement and recruitment rates were estimated from experimental trays that were left in the field and surveyed after 2 weeks (complete experiment was repeated 7 times throughout 1 year). Third, mortality, due to predation, was assessed by covering 50% of the trays with a 4-mm mesh-size screen that excluded large predators (i.e., fishes, shrimps). Fourth, habitat colonization rates were evaluated by quantifying the arrival, into open trays, of large juveniles (secondary dispersal). The most abundant species in this system (Paraxhantus barbiger, Cancer setosus, Taliepus dentatus and Pilumnoides perlatus) displayed clear habitat preferences at the time of settlement, evidenced by differences in density of recruits among habitats. Recruitment regulation by predation seemed to explain the observed patterns in only one case. For most species, however, evidence of ontogenetic change in the use of habitat, through active habitat redistribution by large juveniles, was detected. Thus, secondary dispersal among habitats seems to outweigh the influence of megalopae's habitat selection and post-settlement mortality as responsible for the observed demographic patterns.